Fungal dimorphism is the ability of certain fungi to switch between two different cellular forms, yeast and mycelial forms, in response to external environmental factors. The pacC/Pal signal transduction pathway responds to neutral and alkaline environments and is also involved in the fungal dimorphic transition. In this study, we investigated the function of the pacC homolog, MripacC, which regulates the dimorphic transition and modulates virulence of the insect pathogenic fungus Metarhizium rileyi. MripacC expression was upregulated under alkaline condition, with increased number of yeast-like cells compared to the number of hyphae cells. A MripacC deletion mutant (ΔMripacC) was obtained by homologous replacement and exhibited decreased blastospore budding, with direct development of conidia into hyphae without entering the yeast-like stage when cultured on alkaline medium. Observation of host hemolymph morphology and analysis of samples to detect the main immune factors revealed a decreased ability of ΔMripacC to evade the host immune system. The results of insect bioassays showed that ΔMripacC had decreased virulence with extended median lethality time. Together, the results suggested that MripacC not only regulated adaptation to acidic and alkaline environments, but also influenced virulence by budding blastospores. This elucidation of the function of MripacC adds to our understanding of blastospore budding and virulence of this fungal pathogen.

真菌二态性是某些真菌响应外部环境因素而在两种不同细胞形式（酵母和菌丝体形式）之间切换的能力。在PACC / PAL信号转导途径响应于中性和碱性环境中，并且也参与了真菌二形过渡。在这项研究中，我们研究了pacC同系物MripacC 的功能，它调节昆虫病原真菌绿僵菌的双态转变和毒力。MripacC表达在碱性条件下上调，与菌丝细胞数量相比，酵母样细胞数量增加。一个MripacC缺失突变体（ΔMripacC ) 是通过同源置换获得的，并且在碱性培养基上培养时表现出芽孢出芽减少，分生孢子直接发育成菌丝而不进入酵母样阶段。观察宿主血淋巴形态和分析样品以检测主要免疫因素显示ΔMripacC逃避宿主免疫系统的能力降低。昆虫生物测定的结果表明，ΔMripacC 的毒力降低，中位致死时间延长。总之，这些结果表明，MripacC不仅调节对酸性和碱性环境的适应，而且还通过芽生孢子影响毒力。本次MripacC功能的阐明 增加了我们对这种真菌病原体的芽孢出芽和毒力的理解。